LOVELOCK - This time of year, many ranchers begin sizing up their hay crop and pastures for fall and winter feed. Alfalfa and alfalfa-grass hayfields are widely utilized as a "hay-stockpile" system. Grazing alfalfa in late summer and autumn provides a high-quality pasture for preconditioning calves, putting body condition on bred cows and flushing ewes. Alfalfa regrowth is a rich source of protein, energy, vitamins and minerals. However, due to the potential for pasture bloat, ranchers should always be cautious when grazing alfalfa-dominated hayfields.
Fall grazing presents some specific challenges. Ruminant livestock grazing lush pastures of alfalfa, clovers and small grains are prone to a condition called "frothy bloat." Rapid digestion of forage containing highly soluble proteins results in a stable foam, which prevents rumen gases from being expelled by normal eructation (belching).
Individual animals or a herd can experience severe symptoms including rapid death. The bloat hazard of alfalfa generally increases with lush, vegetative growth, during cool weather (spring or fall frosts), rain, with high soil fertility, but can occur any time during the summer. For season-long grazing, the rumen microflora can adjust such that an animal becomes bloat-tolerant. However, rapid changes in diet quality (such as moving cows from dry grass to lush alfalfa) are risky.
A particularly risky time for grazing alfalfa is immediately following frost. Immediately following a "hard" freeze (defined as adequately cold to rupture cell walls) concentrations of soluble proteins and sugars are very high in the alfalfa forage, which increase its risk for bloat. In general, the forage becomes safer to graze after the stems have collapsed and dried for several days after freezing.
How do you prevent or control bloat? A number of products are promoted as "bloat preventative," including specific alfalfa varieties, ionophores and mineral mixes. However, the most studied and effective treatment is Poloxalene (Bloatguard) - combined with good animal health practices such as mineral supplementation and vaccinations.
Livestock should be fed dry roughage before turning out on alfalfa pasture. The pasture should be dry, and grazing should be continuous rather than frequent corralling or movement. Paddock rotation should occur in the afternoon. The animals should be monitored multiple times daily initially and daily thereafter. The intake of Poloxalene should be monitored, as intake will vary among animals and days
In summary, the value of alfalfa pasture in the fall is very high if the risk of pasture bloat can be controlled. Aside from bloat-inducing crops, bloat is a complex response in terms of pre-existing health conditions and mineral status of livestock. A good description of bloat and its prevention are in the Cattle Producer's Library (http://www.csubeef.com/dmdocuments/625.pdf ).
Source: Dennis Cash and Rachel Endecott from Montana State Extension
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